Fuel additive composition and its preparation

ABSTRACT

A fuel additive composition for the reduction/removal of vanadium-containing ash deposits in gas turbines and other by combustion of vanadium-containing fuel driven apparatuses, which composition as its active ingredient comprises a compound of a metal capable of forming a vanadate with vanadium of said ash deposits is disclosed.

TECHNICAL FIELD

The present invention relates to a fuel additive composition for thereduction/removal of vanadium-containing ash deposits, a process for thepreparation of such a composition and the use of certain inorganicoxygen-containing metal compounds as a component of such a composition.More particularly the present invention relates to a fuel additivecomposition for the reduction/removal of vanadium-containing ashdeposits in gas turbines and other by combustion of vanadium-containingfuel driven apparatuses, a process for its preparation and the use ofcertain inorganic oxygen-containing metal compounds as an activecomponent thereof.

BACKGROUND ART

Fuels such as unrefined crude oil and residual oil containing largeamounts of impurities, which result in corrosive deposits in apparatusesdriven by the combustion of such fuel. One such impurity is vanadium,which forms catastrophically, corrosive low-melting slag. Said slag candestroy vital parts within a short time. Crude oils usually containvanadium in an amount within the range of 1-500 ppm depending on thesource of the oil. Because of its origin as a concentrate from therefining process, residual oil contains several times more vanadium thanthe crude from which it is derived. Combustion of suchvanadium-containing fuels primarily results in the formation of vanadiumpentoxide, V₂O₅, which melts at about 675° C. In molten state V₂O₅behaves as an excellent solvent for e.g. the metal oxides that hightemperature alloys used in the hot section of gas turbines form in orderto protect their surfaces. Thus molten V₂O₅, acting as a solvent, stripsaway said metal oxides. The metal atoms on the surface of the gasturbine section in contact with the combustion gases respond by forminga new layer of oxide coating which is again stripped away by the V₂O₅and so on.

In gas turbines metal temperatures can be higher than 1000° C. at whichtemperatures corrosion can proceed very fast so that the hot section maybe destroyed within a week if no measures are taken to inhibit thecorrosion cycle.

In order to overcome the corrosion problems caused by V₂O₅ the so-calledoil soluble magnesium products were developed. These products are basedon the ability of magnesium compounds to react with V₂O₅ to form avanadate. Early products belonging to this group contained magnesiumnaphthenates which in the next step of development were replaced bycompositions based on magnesium sulfonates. The third generation of oilsoluble magnesium products comprises magnesium carboxylate products.

Thus, for instance, U.S. Pat. No. RE 32653 discloses a method for thepreparation of a magnesium-containing complex by heating, at atemperature above about 30° C. a mixture consisting essentially of

-   -   (A) at least one of magnesium hydroxide, magnesium oxide,        hydrated magnesium oxide or a magnesium alkoxide;    -   (B) at least one oleophilic organic reagent consisting        essentially of an aliphatic cycloaliphatic or aromatic        carboxylic acid containing at least eight carbon atoms or an        ester or alkali metal or alkaline earth metal salt thereof;    -   (C) water; and    -   (D) at least one organic solubilizing agent for component B.

The oil soluble magnesium products are added to the fuel in an amountsufficient to convert V₂O₅ to magnesium orthovanadate, Mg₃V₂O₈, whichmelts at above 1100° C. Said temperature is below the typical gasturbine temperature when introducing the additive composition in thecombustion chamber, but above the turbine gas inlet typical temperaturedue to the flame cooling process. Thus there will be no liquid V₂O₅ thatwill act as a solvent for the alloy surface metal oxides and thuscorrosion caused by V₂O₅ is inhibited.

The first generation of oil soluble magnesium products had aconcentration of magnesium as low as about 4%. The concentration wasincreased in the second generation up to about 14% magnesium and in thethird generation the concentration could be raised further. However,there is a continued need for fuel additive compositions with stillhigher concentrations of magnesium or other metals capable of formingvanadates having a melting point above that of vanadium pentoxide.

Moreover, these prior art compositions give a dense vanadate deposit theremoval of which may cause some trouble.

As an alternative to oil soluble magnesium products U.S. Pat. No.4,412,844, issued Nov. 1, 1983, suggests oil dispersible aqueousdispersions of magnesium hydroxide comprising in percentages by weight:

-   -   (a) 20-70% magnesium hydroxide having particle size from 1.0-50        microns;    -   (b) 29-79% water;    -   (c) 1.0-8.0% of a water-dispersible, oil-soluble, water-in-oil        emulsifying agent having an HLB value of from 4-10;    -   (d) 0.1-6% of a water-soluble, oil-dispersible emulsifying agent        having an HLB of from 20-40.

Such slurries do not allow chemical high efficiency inhibition for ashmelts due to the large crystal size. This patent states the preferredparticle size to be in the range of about 30-2 microns, which makes thecomposition only practically applicable per se to boilers. Thus it isexpressly stated that the magnesium hydroxide slurry specificallydisclosed in the working example “would be utilized to control vanadiumcorrosion in a utility boiler”.

In addition such slurries have a limited stability.

Accordingly, it is an object of the present invention to provide a fueladditive composition containing a high concentration of magnesium orother metal capable of forming vanadates having a melting point abovethat of vanadium pentoxide.

It is another object of the present invention to provide a fuel additivecomposition, which on use gives a porous vanadate deposit that is easilyremoved.

It is a further object of the present invention to provide a fueladditive composition, which is stable for a long time such as 12 monthsand longer at ambient temperature.

These and other objects are achieved by means of the fuel additivecomposition and the process for its preparation according to the presentinvention.

SUMMARY OF THE INVENTION

The present invention is based on the discovery that crystallineparticles of inorganic oxygen-containing metal compounds which whensuddenly being subjected to high temperatures almost “explosively”liberate a gaseous substance by evaporation, such as water vapour orcarbon dioxide in case of e.g. magnesium hydroxide and magnesiumcarbonate, respectively, and are converted to particles of thecorresponding metal oxide having a structure of increased porosity andreduced density when compared to a corresponding oxide prepared byevaporation of gas at considerably lower temperatures. This makes theoxide better suited for reaction with vanadium pentoxide will percolateeasier into the more porous particles. The presence or formation of suchmore porous particles admits a faster chemical reaction due to the factthat the ions of V₂O₅ can travel much faster from the surface of theporous particles along the pores surface of the lattice of saidparticles as vanadate forms than in the denser lattice of non or lowporous crystalline oxide.

It was also surprisingly found that when using an inorganicoxygen-containing metal compound, which liberates a gaseous substance byevaporating when being suddenly subjected to the heat of a combustionflame, or a porous low density oxide with a particle size distributionessentially within the range of from 0.1 to 2 micron as the activeingredient of a fuel additive composition the vanadate deposit formedwas much easier to remove than the vanadate deposit formed when usingprior art compositions.

The said particle diameter less than 1-2 μm as a measurement of particlesize is just a rough indicative measurement, as total mass, density,shape and porosity are important “size” properties to be considered asoptimizing a fuel additive dispersion and its functional properties onash melts and corrosion inhibition as well as deposit problemsconcerned. The optimal “size” in all the size dimensions named willminimize deposit buildups due to the particles kineticadsorption/desorption rate, preferably approaching 1.0 and therebyavoiding high adsorbing atomized and <˜100 nm and avoiding highimpaction rate into deposit by dense particles above the upper, >−1000nm, micron sized limit.

Moreover, it was found that by proper selection of the dispersingsystem, for an oil soluble solvent system, avoiding water to the largestextent possible and using a specific process for the preparation of thefuel additive composition, it was possible to increase the level of theconcentration per volume unit of the metal to a level not having beendisclosed previously for submicron and nano-sized additives. Thus,according to the invention a combination of at least one liquid selectedfrom the group consisting of liquids soluble in oil on one hand and atleast one dispersant selected from the group consisting of low molecularweight dispersants and high molecular weight dispersants on the other isused as the dispersing system.

Thus, in accordance with a first aspect of the present invention thereis provided a fuel additive composition for the reduction/removal ofvanadium-containing ash deposits in gas turbines and other by combustionof vanadium-containing fuel driven apparatuses, which composition as itsactive ingredient comprises a compound of a metal capable of forming avanadate with vanadium of said ash deposits, which composition comprises

-   -   a) as said compound of a metal capable of forming a vanadate        with vanadium of said ash deposits al) an inorganic        oxygen-containing compound of said metal in particle form, which        oxygen-containing compound, when heated up in a combustion        flame, liberates a gaseous substance by evaporation and forms        the corresponding metal oxide having a crystalline porous low        density structure, or a2) said corresponding metal oxide having        a crystalline porous low density structure, said inorganic        oxygen-containing compound al) and said corresponding metal        oxide a2) having a particle size distribution essentially within        the range of from 0.1 to 2 micron, preferably from 0.1 to 1        micron and said corresponding metal oxide a2) having a density        of at most 2.0 g/cm³, dispersed in    -   b) at least one liquid selected from the group consisting of        liquids soluble in oil, by means of    -   c) at least one dispersant selected from the group consisting of        low molecular weight dispersants and high molecular weight        dispersants.

According to another aspect of the present invention there is provided aprocess for the preparation of a fuel additive composition according tothe invention, which process comprises

mixing a powder of an inorganic oxygen-containing compound of a metalcapable of forming a vanadate with vanadium of ash deposits fromvanadium-containing fuel and which inorganic oxygen-containing compoundwhen heated up in a combustion flame liberates a gaseous substance byevaporation to form the corresponding oxide having a crystalline, porouslow density structure or a powder of said oxide having a crystallineporous low density structure into a mixture of at least one liquidselected from the group consisting of liquids soluble in oil with atleast one dispersant for said inorganic oxygen-containing compound oroxide selected from the group consisting of low molecular weightdispersants and high molecular weight dispersants using shear forces toform a homogenous pumpable premix and

subjecting the premix to a treatment comprising size degradation anddispersant coating to a particle size distribution of the inorganicoxygen-containing metal compound and oxide essentially within the rangeof from 0.1 to 2 micron, preferably from 0.1 to 1 micron, undercentrifugal or oscillation forces in the presence of a grinding mediumand/or ultrasonic treatment until a plot of the sediment height insamples taken periodically during said treatment and centrifuged at afixed rate for a fixed period versus time plateaus and the viscosity hasdecreased and come into a steady state.

In accordance with a further aspect of the present invention there isprovided the use of an inorganic oxygen-containing compound of a metalselected from the group consisting of metals capable of formingvanadates having a melting point within the range of from 650° C. to2000° C. with vanadium of ash deposits from vanadium-containing fuel,which inorganic oxygen-containing compound when heated up in acombustion flame liberates a gaseous substance by evaporation to formthe corresponding oxide having a crystalline, porous low densitystructure, or the corresponding oxide obtained by heating the inorganicoxygen-containing compound at a temperature which is high enough to givethe oxide in crystalline porous low density state but is below themelting point of the oxide, said inorganic oxygen-containing compoundand said crystalline porous low density oxide having a particle sizedistribution essentially within the range of from 0.1 to 2 micron,preferably from 0.1 to 1 micron, as a component of fuel additivecompositions for the reduction/removal of vanadium-containing ashdeposits.

DETAILED DESCRIPTION OF THE INVENTION

Vanadium-containing fuels are used within several fields of apparatusesdriven by the combustion of fuel. The corrosion problems caused by thepresence of vanadium may be most serious in the case of gas turbines butsuch problems also exist in connection with e.g. boilers and dieselengines, wherein the metal temperatures are lower than in gas turbinesand relatively less hazardous but still serious corrosion problemscompared to gas turbines exist.

According to the present invention the metal of the inorganicoxygen-containing compound or oxide to be used in the invention shouldbe chosen so that on reaction with the vanadium pentoxide a vanadate isformed that has a melting point exceeding the temperature at which thecomposition is used. Thus, in case of gas turbines a metal should bechosen the melting point of the vanadate thereof preferably exceeds1100° C. Examples of such metals are magnesium the vanadate of whichmelts above 1100° C. and yttrium the vanadate of which has a meltingpoint above 1800° C., magnesium being the preferred metal of these twometals for economical reasons. Examples of other vanadates havingmelting points enabling their use in the compositions according to theinvention to be used in connection with apparatuses of lower temperatureare among others, solely or in combinations, aluminum, zirconium,manganese, iron, copper, nickel and calcium. Often other metals thane.g. magnesium are either both rear and expensive or are environmentalpolluters, e.g. manganese etc.

Depending on the specific field of use generally metals capable offorming vanadates having a melting point within the range of from 650°C. to 2000° C.

Due to contaminants present in the fuel the vanadates formed may becontaminated therewith resulting in a decrease or an increase of themelting point in comparison with 100% pure vanadate. Considerationshould be paid thereto when selecting the metal compound or oxide usedin the composition according to the present invention.

In accordance with one embodiment of the fuel additive compositionaccording to the present invention the active ingredient thereofcomprising an inorganic oxygen-containing compound of a metal capable offorming a vanadate with vanadium of ash deposits is a hydroxide of saidmetal which hydroxide when heated up in a combustion flame is convertedto the corresponding oxide having a crystalline porous low densitystructure.

As indicated previously, hydroxides such as, for instance, magnesiumhydroxide, may be dehydrated almost “explosively” at very hightemperatures (over 1000° C. and below 2800° C.) to form thecorresponding metal oxide. Unlike the oxides formed by dehydration ofhydroxides at lower temperatures (such as just above the dehydrationpoint of 350° C. for the conversion of magnesium hydroxide to magnesiumoxide) resulting in oxides with a more dense crystalline structure theoxides formed at the higher temperatures [below the upper limit in the“dead burned” range where the oxide density closely approaches themaximum density] are more porous and have a less dense crystallinestructure than else.

According to another embodiment of the fuel additive compositionaccording to the present invention said inorganic oxygen-containingcompound of a metal capable of forming a vanadate with vanadium of ashdeposits is a metal carbonate. When suddenly being heated at hightemperatures such as in a combustion flame the carbonate will liberatecarbon dioxide and form the corresponding metal oxide having acrystalline porous low density structure analogously to the formation ofthe oxide from an hydroxide at very high temperatures.

According to a further embodiment of the fuel additive compositionaccording to the present invention said compound of a metal capable offorming a vanadate with vanadium of ash deposits is a metal oxide havinga crystalline porous low density structure. Such oxides may, forinstance, be prepared from the corresponding hydroxides or carbonates byheating at a high temperature. In order to obtain maximum porosity ofthe oxide the conversion of the hydroxide or carbonate should be carriedout below the point at which the oxide tends to increase in density, butclose thereto and far below it starts melting. Above said point at whichthe oxide “tends to start melting” the pore structure continuallydecreases as approaching the critical melting point, at which maximumdensity will be reached, for e.g. magnesium oxide at 2750° C. Such aheat treatment to achieve minimum porous density oxide may be performedby passing a dry powder of an optimal size distribution of the hydroxideor carbonate through a flame having a temperature suitably adapted belowthe density decreasing point of the oxide as indicated above.

Alternatively, low density metal oxides may also be prepared by suddenlysubjecting submicron sized crystals of an inorganic oxygen-containingmetal compound, preferably a hydroxide or a carbonate, which when heatedto a high temperature liberates a gaseous substance by evaporation, toheating at an appropriately high temperature in an oven. Thus, forinstance, the present inventors rapidly heated sub-micron sizedparticles of magnesium hydroxide in an oven at a temperature of 1000° C.for a short time which resulted in the conversion of the magnesiumhydroxide into magnesium oxide having a density of ˜1.4 g/cm³. Similarheating of magnesium carbonate in an oven at a temperature of 1300° C.resulted in magnesium oxide having a density as low as 1.03 g/cm³

According to the present invention the low density metal oxide shouldpreferably have a density of at most 2.0 g/cm³, more preferably below1.5 g/cm³ and most preferably below 1.0 g/cm³.

The inorganic oxygen-containing metal compounds and porous low densitymetal oxides incorporated in the fuel additive composition according tothe invention should have a particle size distribution essentiallywithin the range of from 0.1 to 2 micron, preferably from 0.1 to 1micron, preferably narrowly distributed close to the optimal size withinthat range of 0.1 to 1 micron. Preferably said compounds and oxidesshould have a particle size optimal distribution which is adapted to bemost effective at the temperature at which a solid, porous metalvanadate is formed and to form ash particles which deposit as littleas-possible [due to thermodynamic surface adsorption and desorptionproperties of the particles] and form as loose a deposit as possible[due to the porosity of the particles and thereby the epitactic andtopotactic deposits lattice build-up structure].

According to the high initial flame maximum temperature in the range of1600-2000° C. before cooling the gas the particle size distributionshould be selected so that the metal vanadates formed in the flame arenot given sufficient time to melt before reaching areas of the apparatushaving a temperature below the melting point of the vanadates. Moreover,the porous oxides added to the fuel are not delayed in their reaction tothe formation of the vanadates in the heat zone compared to the porousoxides formed from, for instance hydroxides or carbonates bypassing theheat zone. This means that in case of gas turbines in which thetemperature of the flame may be as high as around 2000° C., a hydroxideor a carbonate should be used which has a particle size which is greaterthan that of the same hydroxide or carbonate to be used in apparatusesoperating at a lower heat zone flame temperature. Furthermore, due totheir higher reactivity surface enlarged porous metal oxides should beused at temperatures lower than those prevailing in gas turbine heatzones, i.e. they may preferably be used in boilers and diesel engines ifan extraordinarily low operating temperature in the heat zone would be adisadvantage of the addition of the heat zone by passing metal hydroxideinto the fuel.

Moreover, it was found that conversion of magnesium carbonate intomagnesium oxide at a given temperature is a slower process than theconversion of magnesium hydroxide to the oxide due to the difference inenergy required to evaporate the carbon dioxide from the carbonate incomparison with water from the hydroxide. This means that in apparatusesworking at relatively low temperatures (e.g. boiler and diesel engines)the use of magnesium hydroxide particles may be the preferred choicewhereas magnesium carbonate might be preferred for use in connectionwith gas turbines having an extremely high temperature in the flame inorder to obtain a low density of the oxide formed.

Of specific importance is that the size of the oxide particles is in therange not below 0.1 micron and not above high density impacting 2micron, preferably exhibiting a particle size distribution injected intothe fuel around 0.4 to 0.5 micron, in order to reduce the depositaccumulation due to the Brown Movement Kinetic affecting the particlessurface adsorption and desorption rate on the deposit surface and thatthe said particles have a surface area including internal pores surfaceinterface area comparable to that of crystalline high density oxideparticles of a particle size far below 0.1 μm to maximize the reactivesurface. Such a high surface area will solely be achievable by porousparticles.

The inventors have noted that dehydration or evaporation of magnesiumhydroxide particles at high temperature causes a split size reductionand volume expansion and agglomeration into a less tight particle sizedistribution depending on the particles individual initial size. Forthis reason the particle size of the particles used in the fuel additivecompositions according to the invention will generally be distributed ina somewhat enlarged size range below and above when using the hydroxidein comparison with the use of a size tailored oxide.

The particles of the inorganic oxygen-containing compound as well as theoxide particles should preferably have a narrow (low variance) particlesize distribution, preferably around a cross section largest distancearithmetic mean in the 0.2 to 0.5 micron range and with a variance for alognormal distribution in the range ˜0.2<δ<˜0.6.

In the fuel additive composition according to the present invention theinorganic oxygen-containing metal compound or oxide particles aredispersed in at least one liquid selected from the group consisting ofliquids soluble in oil.

Contemplated for use in the fuel additive composition according to theinvention are liquids selected from the group consisting of mineraloils, synthetic oils, highly aromatic naphtha, diesel oil, vegetableoils, esterified vegetable oils, animal oils and esterified animal oils.

Examples of vegetable oils and esters thereof to be used in the fueladditive compositions according to the invention include, but are notlimited to, peanut oil, coconut oil, corn oil, linseed oil, rape-oil,palm oil, sunflower oil, olive oil, tall oil and esters thereof, thepreferred representative thereof being rape-oil methyl ester (RME).

Examples of animal oils to be used in the fuel additive compositionsaccording to the invention include, but are not limited to, fish liveroil, train-oil and liquid modified fat from slaughter-houses.

The preferred representatives of the liquids soluble in oil to be usedin the present invention are diesel oil and rape-oil methyl ester.

According to the present invention the inorganic oxygen-containing metalcompound particles or metal oxide particles have become dispersed in atleast one liquid which, as stated above, is selected from the groupconsisting of liquids soluble in oil by means of at least one dispersantselected from the group consisting of low molecular weight dispersantsand high molecular weight dispersants.

The term “low molecular weight dispersants” as used here and in theclaims is used to designate dispersants having a molecular weightusually within the range of from 1.000 to 2.000g/mole. In addition,dispersants may be classified to manifold properties as described below.

The term “high molecular weight dispersants” as used here and in theclaims is used to designate dispersants having a molecular weightusually within the range of from 5,000 to 30.000 g/mole.

In addition. the conventional low molecular weight dispersants arecategorized according to their structure as anionic, cationic,amphoteric and nonionic. Their efficiency is defined by a) absorption ofpolar groups to the surface of the particles to be dispersed and b) thebehavior of a non-polar chain of the medium surrounding the particle.

The dispersant industry supplies a huge variety of efficient stericdispersants that enables stable solid particle dispersions for colloidoil and aqueous systems. A colloid is a liquid droplet or a solidparticle in the size range of at most 1-2 Am but normally submicron orin the range of one molecule to many molecules forming a size of 2-999nm in average diameter. Steric dispersants adsorb and coat the particlesurfaces. A surface is an interface between two non-soluable compounds,one liquid and one solid state or two liquid states. As no interface orsurface occurs between the dispersant-particles-layer-tails penetratinginto the particles ambient solvent the colloid dispersion is a truedispersion formed of particles and such dispersions is commonly definedas a micelle dispersion. A huge group of steric dispersants formsmicelles both in oil and water systems.

Most steric dispersants form micelles in a selected oil soluble solvent,when the hydrophobic tail penetrates into the solvent. The stability ofsuch dispersions is depending on many different forces defining thestability boundaries for the other unit tail. The other said molecularhydrophilic tail adsorbs to the particle surface and will be bondable tothe surface of the particle in many different ways due to the kind of(1) anchor groups, (2) the number of repeating units in the polymer and(3) if the dispersant is a homo polymers dispersants whereas therepeating units are of one kind or is a co-polymer of two differentkinds and (4) the electrostatic properties.

The known art of the described colloid dispersion systems admits asuitable tool to tailor a stable composition of solid particles suitableas a fuel additive. In the range of suitable compounds magnesiumcarboxylates and magnesium sulfonates has been widely used to createstable metal oxide dispersions in fuel additives. In the disclosedinvention the kind of dispersants suitable is enlarged to admit higherconcentrations of stable solid dispersions. Among others we have testedHypermer® LP4 (amine derivate of a fatty acid condensation polymer, fromUNIQEMA, Everberg, Belgium) EFKA 4010 (modified polyurethane, from EFKAInc., Heerenveen, the Netherlands) and Rhodafac® RE 610 (nonylphenolethoxylate based phosphate esters, from Rhodia Inc, France). All ofthese dispersants among others fulfill the claim to form stabledispersions of magnesium oxides and magnesium hydroxides and otherparticles if a suitable solvent and dispersion technology is applied.

The selection of a dispersant for a specific application has to be donedue to the different claims of stability due to ambient boundaries i.e.,solid concentrations, temperature, g-forces and the desired viscosityfor the composition. To achieve maximum particle concentration thedispersant layer that coats the particles has to be thin. This isachieved by a small low molecular weight dispersant as characterized byRhodafac® RE 610 having two tail units penetrating into the solvent orHypermer® LP4. When the volume of solvent in the composition increasesand the particle concentration is lower it is suitable instead to choosea high molecular weight dispersant for instance EFKA 4010. When lowparticle concentrations are desired other dispersants may be preferablyapplied, but for such applications the particle size range is of basicimportance due to solvent molecules Brown Movement Kinetics. In additionsimple non-steric solely and electrostatic dispersants, such as lowmolecular waxy compound e.g. modified or non modified lanoline extractsfrom sheep wool fat-layer may be applied.

High molecular weight dispersants have pendent anchoring groups, whichadsorb to the surface of the particles to be dispersed. Their mechanismof action is by hydrogen bonding, dipole-dipole interactions or Van derWaal forces. The polymeric framework is sufficiently great to give aneffect called sterical stabilization.

The preferred dispersants to be used in the present invention areanionic and amphoteric low molecular weight dispersants.

Although, anionic low molecular weight dispersants to be used in thepresent invention include magnesium soaps of carboxylic and sulfonicacids. Such dispersants and comparable dispersants containing magnesiumare not preferable, as they may comprise atom sizes magnesium thatdepart from the scope of porous oxides feature, as a partial or totaldisadvantage to the aimed invention.

The fuel additive composition according to the present invention willgenerally comprise the submicron or nano-sized inorganicoxygen-containing metal compound or oxide (component a)) in aconcentration of from 10 to 65% by volume, preferably from 20 to 50% byvolume and more preferably from 30 to 50% by volume, and most preferablyfrom 40 to 50% by volume, calculated on the total volume of thecompositions, the balance to 100% by volume essentially consisting ofcomponents b) and c) and possibly a minor amount of water (generallyless than 0.5% by volume) such as moisture emanating e.g. from the useof not fully dry starting materials, such as the hygroscopic substancemagnesium hydroxide or deliberately added to regulate the viscosity andstability of the composition.

The upper limit of the concentration of inorganic oxygen-containingcompound or oxide in each specific case is defined by the particlevolume size and specific dispersants depletion limit due to the specificparticle size that may destabilize the dispersion. Thus the upper limitwill increase with increasing average particle size. Thus, for instance,the upper limit will be around 50% by volume in case of particles havinga particle size low variance distribution, as a distribution havingvariance from ˜0.2 to ˜0.6 for the log-normal distribution around a meansize from 500 to 200 nano-meters (nm) respectively

The volume ratio component b) to component c) generally depends on thespecific substances used as those components and the amount of particlesto be dispersed. The optimum ratio in each specific system may easily bedetermined in a series of experiments varying said ratio for whichexperiments no inventive activity should be required.

The fuel additive composition according to the invention is preparedaccording to said another aspect of the invention by means of theprocess according to the invention, which process comprises

mixing a powder of an inorganic oxygen-containing compound of a metalcapable of forming a vanadate with vanadium of ash deposits fromvanadium-containing fuel and which inorganic oxygen-containing compoundwhen heated up in a combustion flame liberates a gaseous substance byevaporation to form the corresponding oxide having a crystalline, porouslow density structure or a powder of said oxide having a crystallineporous low density structure into a mixture of at least one liquidselected from the group consisting of liquids soluble in oil with atleast one dispersant for said inorganic oxygen-containing compound oroxide selected from the group consisting of low molecular weightdispersants and high molecular weight dispersants using shear forces toform a homogenous pumpable premix and

subjecting the premix to a treatment comprising size degradation anddispersant coating to a particle size distribution of the inorganicoxygen-containing metal compound and oxide essentially within the rangeof from 0.1 to 2 micron, preferably from 0.1 to 1 micron, undercentrifugal or oscillation forces in the presence of a grinding mediumand/or ultrasonic treatment until a plot of the sediment height insamples taken periodically during said treatment and centrifuged at afixed rate for a fixed period versus time plateaus and the viscosity hasdecreased and come into a steady state.

Metal compound particles to be used in the process according to thepresent invention should not contain crystal water and have a lowmoisture content, if necessary obtained by a drying process, preferablya moisture content far below 0.5% by weight.

The particle size of the metal compound or oxide particles should not beexceedingly greater than the size of the particles of compositionprepared by means of the process and generally particle sizes within thesubmicron range should be used, but small particles of a substantialamount below 0.1 microns easily adsorbing the deposit areas and having alow desorbtions rate should be avoided.

According to a preferred embodiment of the process according to thepresent invention the particles of the metal compound or oxide are addedto a vessel containing a mixture of said at least one liquid selectedfrom the group consisting of liquids soluble in oil and at least part ofsaid at least one dispersant under mixing to form a premix allowing thetemperature to rise during the mixing, e.g. to a temperature within therange of from 50° C. to the upper limit ˜85° C. defined by thecentrifugal forces and the viscosity to avoid cavitation of the grindingmedia in order to reduce the viscosity of the premix.

For the procedure of the second step of the process according to thepresent invention preferably a basket mill is used. Such mills areavailable on the market and are, for instance, sold in different modelsunder the trade name Turbomill by Mirodur SpA, Aprilia, Italy.

The grinding media used are e.g. small zirconium balls, the diameter ofwhich is chosen in accordance with the intended particle size of themetal compound and oxide particles, respectively, after grinding so thatsaid diameter is increased when larger particles are wanted. Generallysaid diameter will be within the range of from 0.8 to 1.2 mm, however,balls of uniform size being used in each specific case. Balls of othermaterials known as suited for use as grinding media, e.g. steel andglass, can also be used in the process according to the invention.

A zirconium ball size of 0.8 mm is, for instance, sufficient to reachthe desired size for e.g. Mg(OH)₂-particles and efficiently disperse theparticles in accordance with the invention.

The premix mentioned above is filled into the basket mill vessel androtating is started and speeded up to full power loading allowingtemperature to rise to about 75-85° C. All moisture that evaporatesduring the basket mill operation should be evacuated from the vessel.

Samples are taken at intervals of 30 to 70 minutes such as 1 hour andcentrifuged at a fixed rate, e.g. within the range of from 2000 rpm to4000 rpm, such as 3000 rpm, for a fixed period within a range of frome.g. 30 minutes to 1 hour, such as 45 or 50 minutes, and the height ofthe sediment of each sample measured. During rotation of the basket theheight of the sediment of the different centrifuged samples will startto decrease rapidly as sampling proceeds. Rotation is continued during aconstant temperature operation phase until the plot of sediment heightversus time plateaus and thereby the basic viscosity has decreased andcome into a steady state.

As an alternative to the rotating basket mill operation grinding may beperformed by means of oscillation buckets. Alternatively or as asupplement to grinding ultrasonic treatment may be applied.

The design of grinding mills commonly supplied has to be adjusted forthe engine effect upwards to achieve at least an accelerative forceabove 50 g on the liquid to reach the limit force needed to override thetensions to disaggregate the present smallest nano particles. Preferably70 g is needed as desired to economically optimize the capacitydispersed per kWh etc.

The liquid lubricant film must hold the balls of e.g. a basket millapart from each other. Otherwise the cavitating balls will degradethemselves rapidly. There is no possibility to achieve static pressureto degrade agglomerates and grind nano-scaled particles. The force heretransmitted, to achieve degradation has to be transmitted to theelectromagnetic interference between particle surfaces and theintermediate liquid.

A media mill optimizing the following parameters preferably achievesthis.

1. Temperature

2. Relative content of solids in the liquid

3. Ball size

4. Ball density

5. Ball volume relative to inlet power to be transmitted.

6. Accelerative force in g-number (Af)

Media disc mills are not suitable as accelerative force achievable is tolow.

Commonly in the color industry applied basket mills e.g. a Turbomill issuitable for the present purpose. But other kinds of mills as e.g. highfrequency oscillation ball media vessels as e.g. the Colorox mill may beapplied. By rotating the ball filled basket in a Turbomill theacceleration force (a) will be distinctly controlled by the rotationspeed.a=(ω² *r*2*π); m/s²   Equation (1)

Where: r=peripheral radius in meter for the basket or a body orbit

-   -   ω=angular velocity=rpm/60=cycles per second=Hertz    -   and 1 Newton=1 m/s²; and Af=a/9.82; g

As recognized by equation (1) the acceleration force is proportional tothe radius for a body motion in a circular orbit and proportional to thesquare power for the angular velocity. Thereby, the needed rpm orfrequency for different orbits to reach the acceleration to override thetension is given by:ω=Square root of (Af*9.82*/r) divided by (2*π*60)   Equation (2)

An acceleration force (Af) of 70 g is preferable to exceed the tensionsin the crystal aggregate. Thereby equation (2) tells us the orbitfrequency for different kind of mills and other kinds of powertransmission facilities. As we decrease the orbit radius to a certainlimit e.g. 10 mm we cannot apply the power by centripetal force as in abasket mill of understandable reasons. Instead an high frequencyoscillatory or vibrato vessel is preferable. A 210 mm radius basketneeds a rotating speed of 546 rpm to achieve a peripheral force of 70 g.A small body in 10 mm radius oscillatory vessel needs a rotation speedof 3541 rpm or 59 Hertz.

To roughly define the velocity property limit to be override fordifferent kinds of force transmission equipment in accordance with theinvented process to prepare the dispersion for the invented compositionwe need the illustrative tube. Imagine a tube that enables to applyaccelerative force in inversed direction for the liquid in one directionand the tube wall in the other direction. Thereby the relative speed andthe tension between the liquid and the tube wall will define the sheerforces interfering the particles. As the entire volume in an oscillatoryvessel will oscillate in small orbits the relative speed will reachapproximately a maximum of twice the peripheral oscillation speed.Thereby the shear force limit will be reach at a frequency of 2504 rpmor 42 Hertz for a 10 mm radius oscillatory vessel instead of saidfrequency of 59 Hertz above for a single small body acceleration of 70g.

In addition ultrasonic methods may be used, as dispersion par se isdesired. Similar to the oscillatory vessel case equation (2) will helpus to define the frequency for different ultrasonic amplitudes orwavelengths to be applied. As a conventional ultrasonic frequency is20-40 kHz for e.g. 35 kHz the desired amplitude is 15 nm, but asubstantially higher amplitude in the range above 1-10 microns is anecessity due to achieve sheer beams for the entire particles and notonly for a small limit part on a particles surface area. The amplitudehas to substantially exceed the particles size to admit surface coatingand particles to cavitate. Thereby, ultrasonic equipment is alsocontemplated for use in the present invention, especially as increasedpower density is needed to achieve efficient fast coating on the smallpart of the very small nano particles to get a fully stable dispersionnot reaggregating.

The invention will now become illustrated by means of a number ofnon-limiting working examples illustrating the preparation and use ofthe compositions according to the invention.

EXAMPLES Materials used in Examples 1 & 2

The magnesium hydroxide used was Ankermag®-HH from MagnifinMagnesiaprodukte GmbH, Austria. The magnesium powder contains >98.0% byweight (wt %) Mg(OH) ₂ and <0.5 wt % water. Specific surface 9-12 m²/gequivalence a mean size for a dense sphere diameter range from 200-260nm or in fact the largest diameter of the thin flakes crystals average˜500 nm. The crystals D50 diameter is ˜900 nm, i.e. the median sizediameters in the distribution. In addition the crystal agglomerate upperlimit diameter is less than approximately 50 microns. The preparationprocess according to the invention admits feeding by much largerparticles, preferably a surface area above >3-4 m²/g.

The dispersant used was Rhodafac® RE 610, from Rhodia Inc, France, whichis characterized by the manufacturer as nonylphenol ethoxylate basedphosphate esters.

Rape-oil methyl ester was supplied by Svenska Ekobränslen AB, Sweden.

Example 1 Preparation of Fuel Additive Composition-Batch of 1000 kg

20 kg of Rhodafac® RE610 and 270 kg of rape-oil methyl ester (RME)having a moisture content of <0.05% by weight were mixed in a dissolvervessel (Disolver DTM49 from Westerlins Maskinfabrik AB, Malmö, Sweden)to a homogenous mixture.

Then 690 kg of magnesium hydroxide powder dried to a moisture content of<0.5% by weight were gradually added under continued mixing allowing thetemperature to rise to about 50° C. to form a premix.

The premix was then transferred to the vessel of a basket mill(Turbomill® 2, from Mirodur SpA, Aprilia, Italy, with an engine effectof 55 kW) containing balls of zirconium having a diameter of 0.8 mm asthe grinding medium and rotation of the basket was started and speededup to full power loading.

The temperature was allowed to increase to 75° C.-85° C., i.e. securelybelow the upper limit where the reduced viscosity achieved by theincrease in temperature will allow the balls of the milling medium totouch each other by chance.

The temperature was kept stable until the samples taken at intervals of1 hour and centrifuged at a rate of 3000 rpm for 50 minutes indicated arapid decrease in the height of the pellet obtained by suchcentrifugation after approximately 4-6 hours, due to operationtemperature and the applied centrifugal force. The basket mill was keptrunning until the premix was fully dispersed which occurred asdecreasing the rotation in accordance to the decrease in the height ofthe pellet obtained by centrifuging samples as above until approaching asteady state. Then additional 20 kg of Rhodafac® RE610 and 20 kg ofrape-oil methyl ester (in addition, if desired 1-5 liter water may beadded per ton to achieve increased stabilization of the particles) wereadded and the grinding process continued for approximately 15 minutes.

The completed process was shut down and the composition liquid waspumped into barrels and samples were collected. If desired for thespecific applications the liquid composition is diluted by RME beforebarreling it up.

The Mg content by ash test was ˜29% by weight and the Mg(OH)₂ contentwas 69% by weight (˜46% by volume) and the upper tail of the sizedistribution was below 1,0 micron and the main particle flakes shown bya standard scanning electronmicroscope were in the range 0.2-0.5 micron.

Example 2 Preparation of Fuel Additive Composition-Batch of 1000 kg

40 kg of a Rhodafac® RE610 and 270 kg of diesel (class 1) were mixed ina dissolver vessel (Disolver DTM49 from Westerlins Maskinfabrik AB,Malmö, Sweden) to a homogenous mixture

Then 690 kg of magnesium hydroxide powder dried to a moisture content of<0.5% by weight were gradually added under continued mixing allowing thetemperature to rise to about 50° C. to form a premix

The premix was then transferred to the vessel of a basket mill(Turbomill® 2, from Mirodur SpA, Aprilia, Italy, with an engine effectof 55 kW) containing balls of zirconium having a diameter of 0.8 mm asthe grinding medium and rotation of the basket was started and speededup to full power loading.

The temperature was allowed to increase to 75° C.-85° C., i.e. securelybelow the upper limit where the reduced viscosity achieved by theincrease in temperature will allow the balls of the milling medium totouch each other by chance.

The temperature was kept stable until the samples taken at intervals of1 hour and centrifuged at a rate of 3000 rpm for 50 minutes indicated arapid decrease in the height of the pellet obtained by suchcentrifugation after approximately 4-6 hours, due to operationtemperature and the applied g-force. The basket mill was kept runninguntil the premix was fully dispersed which occurred as decreasing therotation in accordance to the decrease in the height of the pelletobtained by centrifuging samples as above until approaching a steadystate. Then additional 40 kg of Rhodafac® RE610 (in addition, if desired1-5 liter water may be added per ton to achieve increased stabilizationof the particles) were added and the grinding process continued forapproximately 15 minutes.

The completed process was shut down and the composition liquid waspumped into barrels and samples were colleted. If desired for thespecific applications the liquid composition is diluted by dieseloilbefore barreling it up.

The Mg content by ash test was ˜29% by weight and the Mg(OH)₂ contentwas 69% by weight (˜46% by volume) and the size distribution of theupper tail was below 1.0 micron and the main particle flakes shown by astandard scanning electronmicroscope were in the range 0.2-0.5 micron.

Example 3 Comparison of Structures of Magnesium Oxide

In order to compare the structure of magnesium oxide having an porousstructure formed by subjecting magnesium hydroxide to a high temperaturewith that of magnesium oxide prepared by dehydrating magnesium hydroxideat a comparatively lower temperature the following experiment wascarried out.

Three samples of magnesium hydroxide powder having a particle sizedistribution of mean 400 nm, an δ=0.4 for the lognormal estimatedcross-section function and a moisture content of <0.5% by weight andequal in weight were used. The samples were rapidly heated in an oven ata temperature of 450° C. 1000° C. and 1300° C., respectively.

Analyses of the 1000° C. treated sample showed that the surface areaincreased from BET 8.66 m²/g for the hydroxide particles to BET, 10.38m²/g for the porous oxide particles. The density decreased fromapproximately 2.3 g/cm³ for the Mg(OH)₂ to 1.36 g/cm³ (measured by apyknometer) for the converted MgO crystals. This is below 40% of thedensity of nonporous MgO of 3.58 g/cm³ and a remarkably low density.

The specific surface area for Mg(OH)₂ and MgO was measured by MultipointSurface Area N²-gas at 77° Kelvin adsorption isotherm and poredistribution. The pore diameter at surface had its distinct highfrequency with as micropores within the range 3.5-6.5 nm for the almostfully dense Mg(OH)₂ and for the converted low density MgO as mesoporeswithin the range of 10-60 nm with the mode-frequency just below 30 nm

It was confirmed by X-ray diffraction (Cu, K; α=1.54 Å) that MgO has asolely crystalline lattice structure whereby the crystals are not to anydegree an amorphous unordered structured crystal. Thereby the expandedand to some extent sintered crystals contain open pores through thecrystal surface as well as closed pores within the crystals due to thelow density and the small 20% increase in specific surface area asloosen ⅗ atoms out of the crystal volume.

The other two samples treated at 450° C. and 1300° C. confirm that theMgO density is temperature sensitive as density decreases by temperaturewithin the temperature range below the high temperature dead burnedrange above approximately 1600° C. Thereby there my be a need to tailorsize low density MgO particles for certain applications as the operatingcombustion temperature will be below the optimal temperature to formdesired low density MgO particles to reduce deposit buildups

Similary, magnesium carbonate was rapidly heated in an oven at atemperature of 1300° C. and the density of the magnesium oxide thusformed was measured by a pyknometer and found to be 1.03 g/cm³

The results of the density measurements together with density valuesfound in literature are summarized in the following table.

Table

Density of magnesium oxide formed by heating magnesium hydroxide andmagnesium carbonate at different temperatures at ambient atmosphericpressure. Density of MgO from Mg Density of Temp. (OH)₂ MgO from MgC0₃[° C.] [g/cm³] [g/cm²] Remark 450 2.13 — 1000 1.36 — 1300 2.45 1.03 27503.58 3.58 from literature

Example 4

A fuel additive composition according to the present invention was usedin a large-scale comparative test in a power plant, wherein twocomparable 120 MW gas turbines were applied in parallel, both being fedwith the same fuel until injecting the composition according to theinvention and a prior art composition (KL 200 from Baker Petrolite,USA), one for each gas turbine with the same present common pumps intothe oil flow on its final short way into the combustion chamber. The gasturbines were completely up kept at onset including new turbine blades.

The fuel additive composition according to the invention used in thisexperiment had a density of ˜1.56 g/cm³ and contained ˜69% by weight ofmagnesium hydroxide particles and thereby 29% Mg by weight having aparticles size distribution around mean ˜300-500 nm with a variance meanfor the lognormal distribution of ˜0.4 and 4% by weight of Rhodafac®RE610 from Rhodia Inc, France and 27% by weight of REM.

KL 200 is a magnesium oxide over-based magnesium carboxylate vanadiuminhibitor with a density of 1.22 g/cm³ containing 20% Mg as specified bythe supplier.

Based on laboratory test figures every second hour the dose rate wasmaintained at the level of 2 grams of magnesium per 1 gram of vanadiuminherent in the washed heavy fuel oil containing 20-30 ppm vanadium and˜2% sulfur.

Inspections were made after each wash cycle.

The wash cycle is the time range from start of operation until the gasturbine needs to be cleaned up for deposits due to technical andeconomical disadvantages from the accumulated deposits of ash compounds.

It was found at the inspections for the 1^(st) wash cycle before autowash that the deposits were easy to remove by hand in case of using thecomposition according to the invention but could not be removed by handin case of using the prior art composition.

During the 1^(st) wash cycle in this comparative large-scale test, theinput-output efficiency rate adjusted by uncontrolled variables shows anincrease in average MWh output per unit oil of approximately 1% in favorto the turbine injected with the additive in accordance with theinvention. Thereby, it was assumed that the gas turbines run in parallelwith the same fuel was comparable. The 1% efficiency difference betweenthe gas turbines was an underestimation of the true benefits of theinvented composition as illustrated in the next paragraph.

During the 4^(th) and 5^(th) wash cycles both turbines were run with theprior art fuel additive to indicate the comparability. A difference wasfound. Instead of the comparison after the 1^(st) wash cycle the 3^(rd)and 6^(th) wash cycles for the gas turbine run by the fuel additiveaccording to the invention were compared to the 4^(th) wash cycle run bythe prior art fuel additive. It was found that the average efficiencyincreased in an amount of at least 2-4% by using the fuel additivecomposition according to the present invention.

Of special interest is the effect occurred as the turbine was tripped onthe day 8 and the booster effect increased the efficiency by more the 2%units.

The volume of the pores in the deposits was estimated before auto wash.By letting a liquid be absorbed into deposit pieces it was found thatdeposits in accordance with the invention were substantially more porousin the range of an additional pore volume for deposit comparablelocations of 30-115% and in accordance with that a decreased density inthe rage up to 25% was reported. In addition the liquid absorbance speedwas much faster for the deposits in accordance with the invention.

Of great importance is the ability of the deposits to absorb aerosolwater during auto wash and booster tripping a gas turbine. Indicativelythis feature is in proper advance for deposits formed by applying theinvented composition as the absorbance of H₂O from ambient 60% relativehumidity air rapidly reaches a steady state of 2.9% compared to theabsorbance of deposits formed by the prior art conventional compositionwhich was more than 10 time less or 0.25% H₂O at room temperature.

Conclusions

The findings illustrated in the examples show and fully explain thebetter off for gas turbine input-output efficiency for the porousMgO-particles applied in accordance with the present innovation to reactin the combustion chamber instead of MgO dense-structured crystals asmainly is inherent in the combustion chamber for prior art compositions.These findings may be generalized to other solid metal-oxides, from thescientific common sense in chemistry and physics. Thereby, additionalmetals not tested may be applied in accordance with the disclosedinvention to reduce the negative efficiency impacts of hard ash depositsin oil power transformation.

As will be apparent to those skilled in the art in the light of theforegoing disclosure, many modifications, alterations and substitutionsare possible in the practices of this invention without departing fromthe spirit or scope thereof as defined in the appended claims.

1. Fuel additive composition for the reduction/removal ofvanadium-containing ash deposits in gas turbines and other by combustionof vanadium-containing fuel driven apparatuses, which composition as itsactive ingredient comprises a compound of a metal capable of forming avanadate with vanadium of said ash deposits, which composition comprisesa) as the active ingredient either al) an inorganic oxygen-containingcompound of said metal in particle form, which oxygen-containingcompound, when heated up in a combustion flame, liberates a gaseoussubstance by evaporation and forms the corresponding metal oxide havinga crystalline porous low density structure or a2) said correspondingmetal oxide having a crystalline porous low density structure, saidinorganic oxygen-containing compound a1) and said corresponding metaloxide a2) having a particle size distribution essentially within therange of from 0,1 to 2 micron, preferably from 0,1 to 1 micron and saidcorresponding metal oxide a2) having a density of at most 2.0 g/cm³,dispersed in b) at least one liquid selected from the group consistingof liquids soluble in oil, by means of c) at least one dispersantselected from the group consisting of low molecular weight dispersantsand high molecular weight dispersants.
 2. Fuel additive compositionaccording to claim 1, wherein said metal is capable of forming vanadateshaving a melting point within the range of from 650° C. to 2000° C. 3.Fuel additive composition according to any of claims 1 and 2, whereinsaid metal is magnesium or yttrium.
 4. Fuel additive compositionaccording to any of claims 1 to 3, wherein said inorganicoxygen-containing metal compounds or oxide has a particle sizedistribution which is adapted to be most effective at the temperature atwhich a solid, porous metal vanadate is formed and to form ash particleswhich deposit as little as possible and form as loose deposits aspossible.
 5. Fuel additive composition according to any of claims 1 to4, wherein said liquid is selected from the group consisting of mineraloils, highly aromatic naphtha, diesel fuel, vegetable oils, esterifiedvegetable oils, animal oils and esterified animal oils.
 6. Fuel additivecomposition according to claim 5, wherein said vegetable oils and estersthereof are selected from peanut oil, coconut oil, corn oil, linseedoil, rape-oil, palm oil, sunflower oil, olive oil, tall oil and estersthereof.
 7. Fuel additive composition according to claim 5, wherein saidliquid is rape-oil methyl ester or diesel fuel.
 8. Fuel additivecomposition according to any of claims 1 to 7, wherein said inorganicoxygen-containing metal compound or oxide comprises from 10 to 65% byvolume, preferably from 20 to 50% by volume and more preferably from 30to 40% by volume, and most preferably from 40 to 50% by volume,calculated on the total volume of the composition.
 9. Fuel additivecomposition according to any of claims 1 to 8, wherein said at least onedispersant is an anionic or amphoteric low molecular weight dispersant.10. Process for the preparation of a fuel additive composition asdefined in any of claims 1-8, which process comprises mixing a powder ofan inorganic oxygen-containing compound of a metal capable of forming avanadate with vanadium of ash deposits from vanadium-containing fuel andwhich inorganic oxygen-containing compound when heated up in acombustion flame liberates a gaseous substance by evaporating to form tothe corresponding oxide having a crystalline porous low densitystructure or a powder of said oxide having a crystalline porous lowdensity structure into a mixture of at least one liquid selected fromthe group consisting of liquids soluble in oil with at least onedispersant for said inorganic oxygen-containing metal compound or oxideselected from the group consisting of low molecular weight dispersantsand high molecular weight dispersants using shear forces to form ahomogenous pumpable premix and subjecting the premix to a treatmentcomprising size degradation and dispersant coating to a particle sizedistribution of the inorganic oxygen-containing metal compound and oxideessentially within the range of from 0.1 to 2 micron, preferably from0.1 to 1 micron, under centrifugal or oscillation forces in the presenceof a grinding medium and/or ultrasonic treatment until a plot of thesediment height in samples taken periodically during said treatment andcentrifuged at a fixed rate for a fixed period versus time plateaus andthe viscosity has decreased and come into a steady state.
 11. Processaccording to claim 10, wherein the size degradation and dispersantcoating is carried out in a basket mill with zirconium balls as agrinding medium.
 12. Process according to claim 11, wherein sizedegradation and dispersant coating is carried out at an accelerativeforce within the range of from 50 g to 70 g on the liquid.
 13. Processaccording to any of claims 11 and 12, wherein only part of said at leastone liquid and/or said at least one dispersant has been used whenpreparing the mixture of said at least one liquid soluble in oil andsaid at least one dispersant, the remainder of the dispersant and liquidbeing added after said graph over the sediment height in samples takenperiodically and being centrifuged at a fixed rate for a fixed periodhas reached a plateau.